The present invention relates to a sheet finisher capable of carrying out case-binding and to an image forming system having therein the sheet finisher and an image forming apparatus.
In the sheet finisher for carrying out case-binding, a cover sheet is cased up for bookbinding, after adhesives are coated on a spine of bundled sheets. An example of an outline of this process will be explained as follows, referring to FIG. 6.
In the process of the case-binding, sheets P supplied from an image forming apparatus and others are stacked on stopper 100 to be aligned. After sheets P in a prescribed quantity are stacked, they are pressed by pressing members 101 from both sides of the sheets in the direction of a thickness of the sheets to be interposed, and the sheets are kept as sheet bundle 110. The stopper 100 is caused to retreat from its location. Adhesives 111 are coated on a spine of this sheet bundle 110, and elevating plate 103 carrying thereon cover sheet 112 is raised toward the spine or lowered. Meanwhile, on the elevating plate 103, there are positioned spine corner forming plates 104 and 104 which form a spine corner on the spine side of the sheet bundle, on both sides of the sheet bundle 110, and spine corner forming plates 104 and 104 are capable of moving in the direction of a thickness of the sheets.
When the elevating plate 103 is raised and the cover sheet 112 is pressed against the spine, the sheet bundle 110 and the cover sheet 112 are bonded together by the adhesives 111. Then, the spine corner forming plates 104 and 104 are moved to the inside from both sides of the sheet bundle 110 to form a spine corner on the cover sheet 112, thus, booklet 115 is obtained.
With respect to coating of adhesives on the aforesaid sheet bundle, adhesives are usually coated in a way wherein a unit including an adhesive coating roller that rotates is moved against a sheet bundle, and the aforesaid roller is caused to touch the spine of the sheet bundle. A part of the aforesaid adhesive coating roller is caused to touch adhesives in an adhesive storing section that stores adhesives, and when the roller rotates, the adhesives are taken out to be supplied.
There is further proposed an apparatus wherein double coating is made possible by coating adhesives in an outward trip and in a return trip, for the thick coating of adhesives on the spine of the sheet bundle for the purpose of an increase of adhesion strength (for example, see Unexamined Japanese Patent Application Publication No. 2005-178187).
Incidentally, if the adhesive coating roller is rotated in the same direction both for the outward trip and the return trip, uneven and non-uniform coating is caused though a coating weight is increased, in the case of the reverse rotation of the adhesive coating roller (counter coating), although the coated surface is excellent when the direction of the rotation of the roller is a forward direction (regular direction coating).
When a booklet is thin, the aforesaid influence is not very conspicuous, but, when a thickness of a booklet grows greater, an air layer is formed on an uneven portion, thereby, positions which lack adhesion partially are generated, which lowers adhesion strength. Therefore, even in the case of the apparatus disclosed in Unexamined Japanese Patent Application Publication No. 2005-178187,it is possible to conduct coating under the condition of regular rotation (regular direction coating) at all times by switching also the rotation direction of the adhesive coating roller when switching the direction of movement of the adhesive coating roller in the case of the second coating.
However, if the direction of rotation of the adhesive coating roller is switched, an adhesive film on the adhesive coating roller is disturbed for some time immediately after the switching of the rotation direction. Thus, if coating is started without taking any actions, the adhesion quality in the period of start coating is lowered and adhesion strength is lowered, which is a problem.
The invention has been achieved in the context of the aforesaid circumstances, and its object is to provide a sheet finisher capable of obtaining excellent coating conditions even in the case of switching the rotation direction so that the adhesive coating roller may constantly be in the state of regular rotation for the direction of movement, when conducting multiple coating on the spine of the sheet bundle, and to provide an image forming system.